Indicator apparatus for indicating notes emitted by means of a musical instrument

ABSTRACT

The sound to be identified is converted into an electrical signal which is applied to an amplifier (11), a filtering circuit (13) and a calculation device (20); the calculation device comprises a microprocessor (21) and associated memories (22,23) comprising a table of the identifiable notes and octaves, so as to work out a representative value of the frequency of the sound to be identified, to control the reading in the table of notes (23a) in relation to the said worked out value and so as to control the display of the note read on display means (27) connected to the calculation device (20).

The present invention relates to an indicator apparatus for notesemitted by means of an instrument.

By instrument is meant here any wind or string musical instruments, thehuman voice, or any other devices producing sounds.

It is known that instruments, and in particular string instruments,require frequent tunings due to variations in temperature or hygrometry,or because of the hysteresis of tensile forces. The tuning can only beachieved by comparing the produced sound to a key note (diapason) or,just simply, by listening to that sound. This, however, pre-supposes aconsiderable experience and a particularly sharp "ear" for music.

Different types of apparatus have already been proposed to tune musicalinstruments by measuring the frequency of the sounds produced by saidinstruments.

Such an apparatus is described in German Patent Application DE No. 1 547594. Said known apparatus comprises a calculating unit to effect thedifference between a digital value representative of the frequency ofthe note to be checked and a digital reference value selected from amemory of a diode matrix type by actuating a keyboard. The differencecalculated is displayed as well as its sign. With such an apparatustherefore, a manual intervention is necessary to select a new referencevalue everytime a note has to be controlled. This makes the apparatusdifficult to use.

Another known apparatus is described in German Patent Application DE No.2 716 910. With this particular apparatus, the frequency of the note tobe controlled is measured and displayed in digital form, by counting thenumber of oscillations for a reference period of about one second. Sucha reference period is relatively long. Moreover, the display of theresult in digital form makes it necessary to effect a mentalnote/frequency or frequency/note conversion.

It is an object of the present invention to propose a device permittinginstantly and without any manoeuvring, to clearly display any noteproduced by way of an instrument, or more specifically, to clearlydisplay the exact note closest to the sound produced by the instrument,with an indication as to the situation of the sound produced withrespect to the displayed note.

It is also an object of the invention to propose a device which can beused by beginners as well as by experienced musicians to control thetuning of their instrument or even to control the accuracy of the notesthat they produce with the said instrument.

Another object of the invention is to propose a device which isrelatively inexpensive, easy to use, and to which extra functions can beadded, for very little cost, which functions are useful when learning amusical instrument.

These objects are attained with a device comprising:

An amplifier for amplifying a signal representing a sound to beidentified, a filtering circuit connected to the output of theamplifier, a calculation device connected to the output of the filteringcircuit for working out a representative value of the frequencycalculated, in which device, according to the invention, saidcalculation device comprises a microprocessor, and memories connected tosaid microprocessor and comprising a table of notes in which arerecorded items of information which represent the identifiable notes andoctaves, the reading of one such item of information in said table beingcontrolled in relation to the measured value of the frequency of thesound to be identified, and display means are connected to saidcalculation device to receive the information read in said table anddisplay that item of information which represents the closest note tothe sound to be identified and the octave in which said sound issituated.

The use of a microprocessor with a memory constituting a table of notes,in which table are recorded all identifiable notes, makes it possible toobtain a display in uncoded form of the note to be identified, and thisinstantly and without any special manoeuvring.

Advantageously, the calculating device comprises means to estimate thedifference between the calculated frequency of the sound to beidentified and the frequency of the closest note read in the table andto work out an information of accuracy depending on that difference, andsaid display means are arranged so as to receive the said accuracyinformation and display it.

Said accuracy information is for example displayed in the form of a +or - sign, or of 0, depending on the sign and amplitude of thedifference between the calculated frequency and the frequency of thedisplayed note.

According to a particular feature of the apparatus according to theinvention, said apparatus comprises time and measure selection meansconnected to the calculating device, which latter comprises means forcounting the pulses delivered by a time base and to issue a triggeringsignal at the end of each time and each measure selected, and indicatormeans are connected to the calculating device to indicate the times andmeasures in response to the triggering signals.

By taking advantage of the resources offered by the microprocessor andby its associated circuits, the apparatus is then given the addedfunction of metronome.

The indicator means can be light indicators of different colors for thetimes and the measures, or they can be sound indicators of differenttones for the times and for the measures. In this last case, the soundsproduced are advantageously notes from the scale, this giving aself-testing possibility by operating simultaneously the soundindicators and the means to display the note produced by the saidindicators.

According to another feature of the apparatus according to theinvention, the calculating device comprises a table of chords in whichare recorded items of information representing predeterminedcombinations of several notes.

The apparatus thus has an added function in that it memorizes scales,arpeggios and chords which are useful to learn how to read music, and tolearn tones, intervals and harmony.

Other particulars and advantages of the apparatus according to theinvention will appear from the reading of the description madethereafter by way of indication, but not as a limitation, with referenceto the accompanying drawings, in which:

FIG. 1 is a general diagram of one embodiment of the apparatus accordingto the invention,

FIG. 2 is a more detailed diagram of the input circuit of the apparatusof FIG. 1, and

FIGS. 3 and 4 are flow-charts relating to different operations performedby means of the microprocessor of the apparatus of FIG. 1.

The sounds to be identified are converted by means of a microphone 15into electrical signals applied to an input circuit 10 which comprisesan amplifier 11, an energy detector 12 and a filtering circuit 13. Theoutput signal of the filtering circuit is applied to a calculationdevice 20.

The calculation device 20 comprises a microprocessor 21, random accessmemories or RAM 22, read-only memories or ROM 23, an input interfacecircuit 24, an output interface circuit 25, and it receives pulses froma time base or clock 26.

For each operating period of the microprocessor (for example 200milliseconds), the detector output signal frequency is calculated andtransferred into a RAM of the calculation device. Then the closestfrequency note to that calculated is located in one 23a of the ROM 23,which contains in the form of a table of notes all the notesidentifiable by the apparatus in the different octaves. The calculationdevice also works out the quantity ε=Δf/f_(n), Δf being the differencebetween the frequency calculated and the frequency of the located note,and it controls the display of said note as well as of a sign +, - or 0depending on whether ε>ε_(o) >0, or ε<ε'_(o) <0, or ε'_(o) ≦ε≦ε_(o). Thequantities ε_(o) and ε'_(o) are predetermined accuracy threshold values.For example, ε_(o) is selected to equal 1% and ε'_(o) to equal -1%.

This display is achieved on a display device 27 connected to the outputinterface circuit 25 of the calculation device. The device 27 is forexample constituted by an alphanumerical display device with liquidcrystals.

The apparatus illustrated in FIG. 1 further comprises coding wheels 30and 31 designed respectively to select times and measures and connectedto the calculation device via an input interface circuit 24. A frequencydivider 32 receives the clock pulses of the time base 26 and is alsoconnected to the calculation device 20.

The coding wheels 30 and 31 are for example, three and two in numberrespectively, each one numbered from 0 to 9. By way of indication, thetime intervals can be graduated linearly from 40 to 208, the graduation60 corresponding to 1 second, whereas each measure can contain up to 32times. The time intervals and the number of times per measure areselected by hand by actuating the coding wheels.

The pulses SI produced by the frequency divider 32 which have forexample a period of 1/300th of a second, are counted by means of thecalculation device 20 which produces a signal ST, each time the valueselected for a time interval is reached, and a signal SM, each time thevalue selected for a measure is reached.

The signals ST and SM are received by indicator means 33 in order tomark the times and measures selected. Said indicator means compriseamplifiers 34, 35 receiving the signals ST and SM respectively andamplifying them. Said amplified signals are applied, on the one hand, torespective light indicators 36, 37 of different colors and, on the otherhand, to respective sound indicators 38, 39 of different tones.Switching means (not shown) are provided to switch on the lightindicators, or the sound indicators or both.

In response to each signaal ST and SM, the light indicators produce aflash of light and the second indicators produce a very short sound. Theapparatus thus acts as a metronome or rhythm generator.

When the apparatus is used for its "note display" function, the timesand measures are indicated only by luminous flashes.

Preferably, the sounds produced by the sound indicators are specificnotes from the scale, but different. Thus it is possible to check thegood working state of the apparatus by a self-test process usingsimultaneously the "note display" function and the "metronome" function,without any other emission of sounds.

It will also be noted that owing to the resources of the microprocessor,the times and measures values can be selected automatically, for exampleby programming rhythms with varied sequences.

It will be further noted that predetermined combinations of notes can berecorded in a chord table 23b, comprised in the ROM or RAM of thecalculation device, each combination constituting a chord, the knowledgeof which is essential to learn harmony.

The apparatus is then advantageously provided with the possibility ofconducting a special chord verification programme.

The chord verification programme comprises a step which consists indefining and recording the successive notes of a chord played by amusician and in finding out whether the chord identified this way isrecorded in the chord table 23b. The display on the device 27 of theidentified chord is performed on the device 27 if said chord is amongstthe prerecorded ones in the table 23b. If not, the display of the word"ERROR", for example, is controlled.

The chord verification programme can also form part of a more generalprogramme of chords sequence, for controlling the performance ofsuccessive chords according to a predetermined sequence.

The structure and different functions of the apparatus have beendescribed hereinabove in general. Examples of embodiments of certainparts of the apparatus and of the execution programmes of the differentfunctions will now be described in more details.

FIG. 2 shows an embodiment of the input circuit 10.

The signals delivered by the microphone 15 are amplified by way of anautomatic gain control amplifier 11 in order to obtain amplified signalsof constant amplitude. This permits to compensate the fading in time ofsounds produced by a musical instrument such as for example, a piano.

A short pulse eliminator circuit 14 is connected to the output terminalof the amplifier 11, the circuit 14 comprising for example a capacitorconnected between the output terminal of the amplifier and a terminal toa reference potential (earth).

The output of the circuit 14 is connected, on the one hand, to theenergy detecting circuit 12, and, on the other hand, to the filteringcircuit 13.

The circuit 12 comprises an integrator 12a to integrate the amplifiedsignal received. The level of the output signal from the integrator 12ais compared to a predetermined threshold value, by means of a circuit12b for example a flip-flop or a comparator, which produces a signal DEwhen this threshold is exceeded. As can be seen hereinafter, the signalDE authorizes the working of the calculation device 20 to identify thenote received by the input circuit 10.

The filtering circuit 13 is designed to eliminate the frequencyharmonics of the note received. To this effect, it comprises low-passfilters 13a, 13b, 13c, 13d, 13e whose cutoff frequencies are the toplimit frequencies of the successive octaves, in the audio field--i.erespectively about 78, 156, 311, 622, 1244, 2488 Hz for example. Otherfilters can be added for the upper octaves.

The outputs of the filters 13a to 13e are connected, on the one hand, torespective threshold detectors 16a to 16e and, on the other hand, tosignal inputs of respective analog AND gates 17a to 17e. A logic circuit18 has inputs connected respectively to the outputs of thresholddetectors 16a to 16e and outputs connected respectively to controlinputs of the gates 17a to 17e.

Each threshold detector 16a to 16e has for example a structure similarto that of the energy detector DE. When the output signal from a filterexceeds the threshold of the corresponding detector, this produces asignal of high level ("1") at the corresponding input terminal of thelogic circuit 17. Said latter selects the AND gate which corresponds tothe low-pass filter with the lowest cutoff frequency through whichpasses a signal of adequate level. Thus, any harmonics of the receivednote which can be found in the higher octaves are eliminated.

To this effect, the logic circuit 18 comprises NON-AND gates 18a to 18ewith two inputs. The gate 18a has an input at logic level 0 and itsother input is connected to the output of the detector 16a. The gate 18bhas its inputs connected to the detectors 16a and 16b and so on up togate 18e whose inputs are connected to the detectors 16d and 16e.

The outputs of the AND gates 17a and 17e are joined by an analog OR gate19. The output signal of the gate 19 constitutes the input signal SE forthe calculation device 20.

FIG. 3 shows the general set-up of the software used to operate thecalculation device, the different programmes used being recorded inprogramme memories forming part of the read-only memories 23.

After the normal system setting-up phase, one at least of the followingprogrammes is conducted:

the "metronome" programme, to indicate predetermined times and measures,

the "single notes determination and display" programme,

the "chord locating and display" programme for finding out whether achord played appears in the chord table.

It will be noted that the "metronome" and "single notes determinationand display" programmes can be performed simultaneously. Moreover, the"chord locating and display" programme includes the essential part ofthe "single notes determination and display" programme.

Reference will now be made to the flow-chart shown in FIG. 4 . The"single notes determination and display" programme consists in thefollowing operations:

testing the presence of DE: this involves checking the presence of thesignal DE which indicates that an adequate level of energy is received,

if DE is received, the frequency f_(i) of the signal SE converted innumerical form by the interface circuit 24 is measured; to this effect,the number n_(i) of passages through zero of the signal SE is calculatedfor a given period, 200 ms for example; each passage through zero isdetected by a change of sign of the signal SE and the period of 200 msis determined by counting the necessary number of pulses from the timebase; the value n_(i) which is measured is stored;

the input parameters to the note table are calculated in relation to thestored value n_(i) ; the note table is set up in octaves and the accessto it is done by octave level if the note is clearly enough situatedwithin an octave, or between two middles of octaves if the note issituated at the limit of two octaves; the method for calculating theparameters of input and access to the note table is as follows: First,the octave concerned is determined. Therefor, the measured value of thefrequency f_(i) is divided by a constant predetermined number K. Thegreatest integer included in the result serves as an address for a firsttable, where the input address e_(i) of the note table section to beexplored is read. Before exploration of the note table, one checkswhether the number corresponding to the frequency f_(i) divided by K isnot too close to the limit between two octaves. If a difference of morethan 9% is found between this number and the limits between octaves, theexploration of the notes table is performed starting from the addresse_(i) corresponding to the beginning of the octave concerned(exploration of the first type). If a difference is found less than orequal to 9%, the exploration in the notes table is performed startingfrom an address e_(i) -k corresponding to the middle of the octave whichis immediately lower (exploration of the second type). The explorationin the note table is finished when the note N_(i) has been determinedwith which the difference between the exact frequency of this note andthe measured frequency is minimum;

the note N_(i) is read and is stored and the precision ε_(i) =(f_(i)-fN_(i))/fN_(i) is calculated, fN_(i) being the exact frequency of thenote N_(i) ; the quantity ε_(i) is compared to positive and negativepredetermined values ε_(o) and ε'_(o) (for example +1% and -1%) andε_(i) =1,0 or -1, depending on whether ε_(i) >ε_(o) >0, or ε'_(o) ≦ε_(i)≦ε_(o), or ε_(i) <ε'_(o) <0, is stored;

the note N_(i) is displayed on the display device 17 together with thesign +, 0 or -, depending on whether ε_(i) =1, 0 or -1;

then, there is resetting, to wait for another detection of energy unlessa chord location is requested; said last condition is checked bycontrolling the value of a signal RA, which value is for examplecontrolled by actuating a key on the apparatus when the "chord locatingand display" programme is requested.

It is presumed that the chords recorded in the chord table arecombinations of two or three notes, the chord table being set up in agroup of chords of two notes and a group of chords of three notes.

The "chords locating and display" programme comprises the followingsteps:

waiting for a note;

when a first note N_(i) is identified and when it has been checked thata chord is to be located, said first note is recorded and the content ofa register [NNI] (number of notes identified) is placed at 1, saidregister being initially set to zero;

then it is checked whether a chord can be located by looking through thecontent of the register NNI;

the content of the register NNI being equal to 1, one returns to waitingfor another note;

when a second note N₂ is identified, it is recorded and the contents ofthe register [NNI] is incremented by one unit (NNI=2);

there is then a possibility of locating a chord in the chord table;

the search through the chord table is effected by comparing successivelyeach chord of two notes of this table with the pair N₁ -N₂, due to theverification NNI=2;

if the chord N₁ -N₂ is found in the table 23b, the register [NNI] is setback to zero and the chord is displayed on the display device 27;

if the chord N₁ -N₂ is not located, the search is continued amongst thethree-note chords listed in the table; if none of these chords comprisesN₁ -N₂ as first two notes, the register [NNI] is set back to zero andthe word "ERROR" is displayed on the device 27; but on the contrary, ifone of the chords of the table starts with the notes N₁ -N₂, one returnsto waiting for a third note;

when a third note N₃ is located, it is recorded and the contents of theregister [NNI] is incremented by one unit (NNI=3);

the search through the chord table is effected in the three-note groupof chords only, because of the verification NNI=3;

if the chord N₁ -N₂ -N₃ is found, the register [NNI] is reset to zeroand the chord is displayed on the display device 27 (which capacity isindeed choosen to be sufficient for this purpose).

if the chord N₁ -N₂ -N₃ is not found, the register [NNI] is reset tozero and the word "ERROR" is displayed on the display device 27.

As already indicated hereinabove, said programme can be completed bychecking, not only that each chord played is listed in the chord table,but also, that the chords are played in a predetermined order, accordingto a recorded sequence.

FIG. 4 also illustrates the different operations of the metronomeprogramme. Said programme is for example used in response to theactuation of a special key which closes a switch interposed between thetime base 26 and the frequency divider 32. The signal produced by thefrequency divider 32 constitutes an interruption signal which triggersoff the performance of the following operations:

incrementing by one unit the contents [RI] of a register RI:[RI]+1→[RI];

reading the value T displayed by the coding wheels 30 and converted intonumber of periods of the interruption signal SI;

comparing the content [RI] of the register RI with the value T;

if [RI]<T, return to the interrupted programme;

if RI=T, incrementing by one unit of the content [RT] of a time registerRT: [RT]+1→[RT]

reset to zero of register RI=[RI]→0;

reading of the value M displayed by the coding wheels 31;

comparing the content [RT] of the register RT with the value M;

if [RT]<M, production of an output triggering signal ST and return tothe interrupted programme;

if [RT]=M, production of an output triggering signal SM, reset to zeroof the register RT [RT]→0, and return to the interrupted programme.

Various modifications and additions may of course be made to theembodiment of the invention described hereinabove.

For example, the frequency f can be calculated by counting the number ofpulses of the time base for a predetermined number of periods of thesignal SE, each period being for example the interval between twosuccessive passages through zero in the same direction.

In addition, in the case of relatively long sounds being measured, asmoothing of the frequency measurement can be introduced into theprogramme as well as a smoothing of the identification of the note.

The operation of frequency smoothing is inserted into the single notesdisplay and research flowchart, before calculating the input parametersin the note table (calculation of f_(i) /K). It is known that musiciansdivide an octave into 12 half-tone intervals, each interval having1.05946 times the frequenncy of the preceding lower halftone, i.e. afrequency about 6% higher. Then the following smoothing process is used;f_(i) being the frequency which has just been measured, the frequency is"smoothed" by giving it the value f_(in) =1/2 (f_(i) +f_(in-1)) if##EQU1## designating the previously determined smooth frequency byf_(in-1). In other terms, a new value f_(i) is taken into account if itdiffers from the preceding value by more than 3%; if not thearithmetical average is worked out between said new value and theprevious value.

The note smoothing operation is inserted before the display of the noteand of its accuracy. This operation consists in conducting a majoritytest on the accuracy provided that the note remains the same three timesin succession. The majority test consists in displaying--if theaccuracy--is determined at least twice out of three times, in displaying+, if the accuracy + is determined at least twice out of three times,and in displaying 0 if the accuracy 0 is determined three times, or ifonce each accuracy +, - and 0 is determined once. In the case where tomeasure a sound, the same note is not obtained three times insuccession, it can be fitting to display the word "ERROR".

I claim:
 1. Apparatus for indicating the presence of musical notes andfor identifying the musical notes detected comprising:means foramplifying input signals corresponding to musical notes to beidentified; filter means connected to said means for amplifying foreliminating harmonics from said input signals; energy detecting meansconnected to said means for amplifying for detecting input signalsexceeding a predetermined threshhold; memory means including at leastone memory for storing items of information representing a table ofmusical notes; means for calculating the frequency and octive of saidinput signal, said means for calculating including microprocessor meansand being connected to said filter means, said energy detecting meansand said memory means, said means for calculating being responsive toinput signals received from said filter means exceeding saidpredetermined threshhold determined by said energy detecting means tocalculate the frequency thereof, said frequency calculated beingemployed to read from said memory for storing items of informationrepresenting a table of musical notes items of information representingthe closest corresponding musical note for said frequency calculated;and means for displaying, in alphanumeric form, said musical note readclosest to each successive musical note in said input signals to beindentified and the octive in which said musical note resides.
 2. Theapparatus according to claim 1 wherein said means for calculatingadditionally comprises:means for determining any difference between saidfrequency of said input signals calculated, and said closestcorresponding musical note read; means for providing indiciarepresentative of any difference determined; and means for supplyingsaid indicia to said means for displaying to cause said indicia to bedisplayed.
 3. The apparatus according to claim 2 wherein said indiciatake the form of a plurality of signs, and selected ones of saidplurality of signs respectively indicate that a difference between acalculated frequency of an input signal and a frequency of a displayedmusical note is a positive value exceeding a predetermined limit, anegative value exceeding a selected limit and a value within a limit. 4.The apparatus according to any one of claims 1, 2 or 3 wherein saidfilter means comprises:a plurality of low pass filter means forreceiving said input signals representing said musical notes to beidentified; a plurality of threshhold detector means for indicating thatinput signals applied thereto exceed a predetermined threshhold, each ofsaid plurality of threshhold detector means being connected to anassociated one of said plurality of low pass filter means; means fordetermining a one of said plurality of low pass filter means having thelowest cut-off frequency characteristic and at least a portion of saidinput signals having a predetermined threshhold level passingtherethrough; and means for inhibiting outputs from remaining ones ofsaid plurality of low pass filter means having cut-off frequencycharacteristics higher than that of said one of said plurality of lowpass filter means.
 5. The apparatus according to any one of claims 1, 2or 3 wherein said energy detecting means includes an integrator meansconnected to an output of said means for amplifying.
 6. The apparatusaccording to claim 3 additionally comprising means for selecting timesand measures, said means for calculating being responsive to said meansfor selecting times and measures to count pulses provided during a timebase and to produce a triggering signal at an end of each time and eachmeasure selected and means connected to said means for calculating forindicating times and measures in response to said triggering signalwhereby metronome and rhythm generator functions may be performed. 7.The apparatus according to claim 6 wherein said means for indicatingtimes and measures include light indicators having a plurality of colorsfor said times and measures.
 8. The apparatus according to claim 6wherein said means for indicating times and measures include soundindicators having a plurality of tones for said times and measures. 9.The apparatus according to claim 8 wherein said plurality of tonescorrespond to notes of a scale.
 10. The apparatus according to claim 1wherein said memory means includes a memory containing a cord table inwhich items of information representing predetermined combinations ofseveral notes are recorded.
 11. The apparatus according to claim 10wherein said means for calculating additionally comprises:means forrecording a plurality of notes identified successively; means forcomparing said plurality of notes recorded with said predeterminedcombinations of several notes present in said cord table; and means forindicating results of comparisons performed by said means for comparing.